The present invention relates to an arrangement for the automatically controlled varying of the relative rotating position of two shafts in an internal-combustion engine, comprising at least one camshaft which can be rotated relative to a shaft driving it, as a function of parameters of the internal-combustion engine, and a driving wheel which drives the camshaft. The driving wheel carries a first toothing or set of gear teeth and, by way of a coupling member which is axially displaceable at least in two end positions, acts upon a second toothing connected with the camshaft. At least one of the toothings is a helical toothing.
It is known to adapt the valve timing of an internal-combustion engine to its rotational speed in order to be able to operate it optimally in a rotational speed range that is as wide as possible. As a result, the torque, the performance, the exhaust emission, the idling action and the fuel consumption can be improved.
One possibility of changing the valve timing during the operation of the internal-combustion engine comprises rotating the intake canshaft in its position relative to the crankshaft driving it by means of a phase converter. For example, European Patent Document EP 0 335 083 shows a coupling member that is axially shifted and which is coaxially surrounded by the wheel driving the camshaft, as a function of oil pressure. The coupling member carries two toothings of which at least one is helically geared and which interact with one corresponding toothing respectively on the camshaft or in the wheel. Disadvantages of this construction are the high expenditures with respect to components for the leading-in and gradual shut-off of the pressure oil as well as the large size.
The British Patent Document GB-21 89 086 shows a camshaft which is coaxially surrounded by a hollow shaft section which carries a can for the actuating of a charge cycle valve. An annular gap constructed and sealed off between the camshaft and the shaft section is filled with an electroviscous fluid (EVF). By feeding an electric voltage between the camshaft and the insulatedly held shaft section, the viscosity of the EVF is increased to such an extent that a rigid coupling is created so that the shaft section rotates synchronously with the camshaft. When the voltage is disconnected, the electroviscous fluid will liquify, whereby the shaft section is uncoupled from the camshaft. With this arrangement, for example, a charge cycle valve can be connected and disconnected, or the valve overlap can be varied between intake valves and exhaust valves. If the valve overlap is varied between intake valves and exhaust valves, this arrangement achieves the same effect that can be achieved by a change of the relative rotating position between an inlet camshaft and an outlet camshaft.
An object of the present invention is to provide an arrangement of the above-mentioned type which reduces the component expenditures and size and has a simple and low-cost construction.
This and other objects are achieved by the present invention which provides an arrangement for automatically controlled varying of a relative rotating position of two shafts in an internal-corabustion engine, the shafts including a camshaft and a second shaft, the camshaft being rotatable relative to the second shaft as a function of parameters of the internal-combustion engine. The arrangement comprises a driving wheel which drives the camshaft and carries a first toothing. A second toothing is connected with the camshaft, with at least one of the first and second toothings being a helical toothing. A coupling member is provided that is axially displaceable between at least two end positions and is arranged between the driving wheel and the camshaft to act upon the second toothing. A stationary intermediate timing gear bearing ring coaxially surrounds the coupling member at least in sections and bounds an annulus formed between the bearing ring and the coupling member. A fluid is provided in the annulus, this fluid having a viscosity which can be changed by application of voltage. An electronic control device is coupled to apply a first output voltage to the fluid, wherein application of the first output voltage to the fluid creates a braking moment that acts on the intermediate timing gear, the braking moment causing an axial force that displaces the intermediate timing gear towards one of the end positions.
One of the principal advantages achieved by the present invention is that the arrangement can rapidly change the relative rotating position and only requires a small number of components, particularly moving components. It also only requires little installation space. The coupling member which is constructed as an intermediate timing gear is surrounded coaxially at least in sections by a stationary intermediate timing gear bearing ring, in which case an annulus is bounded between the two parts which is filled with an electroviscous fluid. An output voltage, which is supplied to this fluid by an electronic control device, changes the viscosity in such a manner that a braking torque acts upon the intermediate timing gear which, because of the helical toothing, causes an axial force which shifts the intermediate timing gear into the direction of a first end position.
A construction of the first and second toothing as helical toothings, as in certain embodiments, increases the rotating angle of the camshaft with respect to the shaft driving it and blocks an unintentional pushing-back of the intermediate timing gear which is the result of an alternating non-uniform camshaft driving torque.
In certain embodiments of the invention, an axially oscillating relative movement of the intermediate timing gear on the camshaft which is caused by this driving torque is effectively damped by a diaphragm spring which is arranged between the camshaft and the intermediate timing gear and, at the same time, applies the spring force required for a restoring.
So that any rotating position can be adjusted between the two end positions, certain embodiments of the invention provide an electroviscous locking bearing between the camshaft and the intermediate timing gear. The electroviscous locking bearing is supplied with an output voltage also from the electronic control device and causes a radial pressure force which results in an axial locking force which counteracts the spring force and compensates it. The annulus as well as the locking bearing are bounded on both sides by commercially available sealing rings which are fixed in a simple manner in the intermediate timing gear bearing ring and on the camshaft.
In certain embodiments of the invention, in the annulus and on a segment of the camshaft assigned to the locking bearing, electrodes are mounted which are in direct contact with the electroviscous fluid. The electrodes are arranged in an insulated manner, in which case, either an electrically non-conductive intermediate layer is used, or the intermediate timing gear bearing ring or the segment are manufactured of a non-conductive material.
Certain embodiments of the invention provide electrically conductive connections by which the electrodes are connected to a high-voltage module of the control device. In this case, the electrode on the segment of the camshaft is supplied by a connection guided centrically into the camshaft, for example, the screwing together of the diaphragm spring and a connection extending from there radially to the electrode. An actual differential angle of rotation between the camshaft and the crankshaft is detected by way of sensors and is fed to the electronic control device. In this control device, optimal differential angles of rotation are stored in characteristic diagrams as a function of parameters of the internal-combustion engine. In lists which are logically linked with the optimal angles, the output voltages are stored.
The arrangement has a simple construction because it employs components which are required also in known oil-hydraulically or electrically operated phase converters.
The intermediate timing gear bearing ring may be constructed as a separate component or as part of the cylinder head.
The required amount of fluid is low because it must be discharged and renewed continuously.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.